Mössbauer spectroscopy of Fe/S proteins

Iron-sulfur (Fe/S) clusters are structurally and functionally diverse cofactors that are found in all domains of life. ⁵⁷Fe Mössbauer spectroscopy is a technique that provides information about the chemical nature of all chemically distinct Fe species contained in a sample, such as Fe oxidation and spin state, nuclearity of a cluster with more than one metal ion, electron spin ground state of the cluster, and delocalization properties in mixed-valent clusters. Moreover, the technique allows for quantitation of all Fe species, when it is used in conjunction with electron paramagnetic resonance (EPR) spectroscopy and analytical methods. ⁵⁷Fe-Mössbauer spectroscopy played a pivotal role in unraveling the electronic structures of the "well-established" [2Fe-2S]^2+/+, [3Fe-4S]^1+/0, and [4Fe-4S]^3+/2+/1+/0 clusters and -more-recently- was used to characterize novel Fe/S clustsers, including the [4Fe-3S] cluster of the O₂-tolerant hydrogenase from Aquifex aeolicus and the 3Fe-cluster intermediate observed during the reaction of lipoyl synthase, a member of the radical SAM enzyme superfamily.